Structural, Electrical and Dielectric Properties of Co–Mn Spinel Nanoferrites Prepared by Co-precipitation Technique

Cobalt manganese nanoceramics with nominal composition Co 1− x Mn x Fe 2 O 4 ( x =0.00, 0.15, 0.30, 0.45, 0.60, 0.75) were synthesized by a chemical coprecipitation technique. The X-ray diffraction patterns revealed the cubic spinel structure. The average crystallite size from the Sherrer formula was in the range of 28 nm–56 nm. The lattice parameter increased with a concentration of manganese. Scanning electron microscopy (SEM) was used for microstructural study. The electrical properties such as electrical resistivity ( ρ ), drift mobility ( μ d ), and activation energy (Δ E ) were measured using a two-probe apparatus in the temperature range 323–573 K. The electrical resistivity decreased with temperature and manganese concentration. The dielectric constant ( ε ′), loss factor or imaginary loss ( ε ″) and dielectric tangent loss (tan δ ) were measured at room temperature using a LCR meter in the frequency range 100 Hz to 5 MHz. All the dielectric parameters decreased with increasing frequency. The AC electrical conductivity ( σ ac ) was calculated from the dielectric measurements. It increases with increase of frequency and manganese concentration. The increase in electrical conductivity may be attributed to the formation of Co +3 and Mn +3 from Co +2 and Mn +3 , respectively, at both A and B sites.